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Scientists at Cambridge have found changes in the brain that are linked to obsessive-compulsive disorder.

The condition is quite common, affecting 2 to 3 per cent of the population, and is marked by obsessions and constantly repeated actions. In the film As Good As It Gets, Jack Nicholson played a novelist with the disorder whose obsessive behaviour made normal relationships almost impossible. He could not get out of bed without tapping his slippers first, and avoided cracks in the pavement while walking down the street.

People with obsessive-compulsive disorder (OCD) may also suffer recurrent, unwanted thoughts and be obsessively concerned with themes of contamination. Some sufferers become locked into a loop of repeated actions, such as washing their hands.

OCD tends to run in families, but the gene responsible has not so far been found. A team from the Brain Mapping Unit at the University of Cambridge decided to look not for the gene, but for effects of the gene on brain structure that might be detectable in patients and in unaffected relations.

To explore this, the team led by Ed Bullmore used magnetic resonance scanning of the brain and measures of individuals’ ability to perform simple tasks involving brain and hand. They scanned the brains of 31 OCD patients, comparing them with 31 first-degree relations who were unaffected by OCD – sisters, brothers, parents, and children – and 31 unrelated healthy people.

The volunteers also completed computerised tests designed to assess their ability, once they had become established in a pattern of repetitive behaviours, to stop performing them.

Both the OCD patients and their close relations did worse on the computer task than the control group, the team reports in the journal Brain. Earlier research has shown similar results, suggesting that when a pattern of actions is established, people with OCD find it hard to stop them.

When the performance on this test was compared with MRI scans, it was found that performing poorly was associated with decreases of grey matter in brain regions important in suppressing responses and habits.

But this was the case both in actual OCD cases, and in close relations who did not suffer the disease, suggesting that there must be additional factors that determine what triggers the condition in susceptible people.

Lara Menzies, the lead author of the paper, said: “Impaired brain function in the areas of the brain associated with stopping motor responses may contribute to the compulsive and repetitive behaviours that are characteristic of OCD.

“These brain changes appear to run in families and may represent a genetic risk factor for developing the condition. The current diagnosis of OCD is subjective and therefore knowledge of the underlying causes may lead to better diagnosis and ultimately improved treatments.”

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